As processes of directly forming positive images by a color diffusion transfer process, there are A) a process of using a combination of a direct positive silver halide emulsion and a non-diffusible compound which can release a diffusible dye corresponding to the reaction in which a silver halide is reduced to silver (hereinafter, this compound is referred to as a negative type dye-providing compound) and B) a process of using a combination of an ordinary silver halide emulsion (a negative-positive responding silver halide emulsion) and a non-diffusible compound which becomes diffusible in countercorrespondence to the reaction in which a silver halide is reduced to silver or a non-diffusible compound which can release a diffusible dye in countercorrespondence to the reaction in which a silver halide is reduced to silver (these compounds are referred to as positive dye-providing compound).
In process A), the compound which is a coupler having a non-diffusible dye as a releasable group and which releases the diffusible dye by a coupling reaction with the oxidation product of a reducing agent (DDR coupler) described, e.g., British Patent 1,330,524, JP-B-48-30165 (the term "JP-B" as used herein means an "examined published Japanese patent publication"), and U.S. Pat. Nos. 3,443,940, 4,474,867 and 4,483,914, and a compound which reduces a silver halide and which releases a diffusible dye by reducing a silver halide (DRR compound) described in U.S. Pat. Nos. 3,928,312, 4,063,312, 4,055,428, and 4,336,322 are used.
In process B),
(1) a hydroquinone series developer and a dye developing agent bonded to a dye moiety (the dye developer is diffusible under an alkaline condition but becomes non-diffusible upon reacting with a silver halide) described in U.S. Pat. Nos. 3,134,764, 3,362,819, 3,597,200, 3,544,545, 3,482,972, etc.,
(2) a non-diffusible compound which releases a diffusible dye under an alkaline condition but loses this ability when it reacts with a silver halide described in U.S. Patent 4,503,137, etc., a compound capable of releasing a diffusible dye by an intramolecular nucleophilic substitution reaction described in U.S. Pat. No. 3,980,479, etc., or a compound capable of releasing a diffusible dye by an intramolecular rearrangement reaction of an isooxazolone ring described in U.S. Pat. No. 4,199,354, etc., or
(3) a non-diffusible compound copable of releasing a diffusible dye by reacting a reducing agent remained without being oxidized by the development described in U.S. Pat. Nos. 4,559,290 and 4,783,396, European Patent 220,746A2, and Kokai Giho 87-6199, etc., is used.
In the foregoing two processes, process B) is preferred for easily obtaining a high sensitivity. However, with process B), it is difficult to reduce the minimum density portion, which is particularly important in an image formation process.
In process B), the density of the minimum density portion (corresponding to a high exposure portion) of a positive image is determined by the competing reactions of the dye-releasing reaction by a reducible dye-providing compound and an electron donor and an oxidation reaction of an electron donor by the oxidation product of an electron transferring agent (formed by the development of a photosensitive silver halide).
Accordingly, for lowering the minimum density while keeping the high density, a technique of making the formation of the oxidation product of the electron transferring agent an optimum state by controlling the development of the photosensitive silver halide is needed.
As silver halide grains which are used for silver halide photographic materials, various grain forms are known, and as one kind thereof, tabular silver halide grains are known.
In regard to tabular silver halide grains, production methods and techniques for using these grains are disclosed in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353 and JP-A-59-99433 and JP-A-62-209445 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), and the advantages provided by the tabular silver halide grains, such as the improvement of sensitivity, including the improvement of color sensitizing efficiency by a sensitizing dye, the improvement of the relation of sensitivity and graininess, the improvement of sharpness by the specific optical property of the tabular silver halide grains, the improvement of covering power, etc., are known.
A heat developable light-sensitive material using tabular silver halide grains composed of (100) crystal planes is disclosed in JP-A-1-161335, but the invention thereof relates to an image-forming process using a developing process which is significantly different from the developing process in the present invention. Also, the effects thereof are significantly different from those of the present invention.
The dislocation of silver halide crystals is described in C. R. Berry, Journal of Applied Physics, 27, 636 (1956), C. R. Berry and D. C. Skilman, Journal of Applied Physics, 35, 2165 (1964), J. F. Hamilton, Phot. Sci. Eng., 11, 57 (1967), T. Shiozawa, J. Soc. Phot. Sci. Jap., 34, 16 (1971), T. Shiozawa, J. Soc. Phot. Sci. Jap., 35, 213 (1972), etc. It is stated therein that the dislocation in a crystal can be observed by an X-ray diffraction method or a low-temperature transmission type electron microscopic method, and various dislocations occur in a crystal as a result of a strain to the crystal.
The influences of the dislocation on the photographic performance are described in G. C. Famell, R. B. Flint & J. B. Chaneter, J. Phot. Sci., 13, 25 (1969), and it is shown therein that in tabular silver bromide grains having a large grain size and a high aspect ratio, the site of the formation of a latent image nucleus has a close relation with a defect in the crystal.
JP-A-63-220238 and JP-A-1-201649 disclose tabular silver halide grains having dislocations introduced therein. It is shown therein that the tabular silver halide grains having dislocations introduced therein are excellent in photographic characteristics such as sensitivity, reciprocity law, etc., as compared to tabular silver halide grains having no dislocation. Also, a photographic light-sensitive material using tabular silver halide grains having dislocations is excellent in sharpness and graininess. However, in these tabular silver halide grains, the dislocation lines are irregularly introduced into the edges of the tabular grains, and the number of dislocations differs in each grain.
A silver halide photographic emulsion comprising a dispersant and tabular silver halide grains having dislocations in the major surface region is disclosed in U.S. Ser. No. 710,346.